Mass is still the standard dose metric applied in the nano(eco)toxicology literature. Greater particle surface area or number may be more relevant dose metrics than mass to represent particle interactions with biological surfaces. This investigation involved exposure of the water flea Ceriodaphnia dubia and the fathead minnow Pimephales promelas to 10, 20, 30, 60 and 100 nm silver nanoparticles. Dose relationships were compared using total measured mass concentration, dissolved concentrations, total surface area and particle number concentration in suspension. Conclusions were that the total surface area dose metric best described the toxicity of the silver nanoparticles. In this case, the surface area dose metric may have described the observed toxicity because as it is related to ion release, the main toxicity driver of these nanoparticles. Particle number may provide a relevant dose metric for particles that are less prone to dissolve, such as nano-gold . The data generated were used to populate a web-based tool where users can enter and visualize data by different dose metrics (mass, size, surface area, particle number) to determine the best relationship.